mm: page allocator: calculate a better estimate of NR_FREE_PAGES when memory is low...

[net-next-2.6.git] / mm / vmstat.c

diff --git a/mm/vmstat.c b/mm/vmstat.c
index a8d6b59e609a390d6e5d33c4560d1cb3a47814b8..355a9e669aaa800d62fa31d2b83110bf76cce9d7 100644 (file)
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -138,11 +138,24 @@ static void refresh_zone_stat_thresholds(void)
        int threshold;
 
        for_each_populated_zone(zone) {
+               unsigned long max_drift, tolerate_drift;
+
                threshold = calculate_threshold(zone);
 
                for_each_online_cpu(cpu)
                        per_cpu_ptr(zone->pageset, cpu)->stat_threshold
                                                        = threshold;
+
+               /*
+                * Only set percpu_drift_mark if there is a danger that
+                * NR_FREE_PAGES reports the low watermark is ok when in fact
+                * the min watermark could be breached by an allocation
+                */
+               tolerate_drift = low_wmark_pages(zone) - min_wmark_pages(zone);
+               max_drift = num_online_cpus() * threshold;
+               if (max_drift > tolerate_drift)
+                       zone->percpu_drift_mark = high_wmark_pages(zone) +
+                                       max_drift;
        }
 }
 
@@ -813,7 +826,7 @@ static void zoneinfo_show_print(struct seq_file *m, pg_data_t *pgdat,
                   "\n        scanned  %lu"
                   "\n        spanned  %lu"
                   "\n        present  %lu",
-                  zone_page_state(zone, NR_FREE_PAGES),
+                  zone_nr_free_pages(zone),
                   min_wmark_pages(zone),
                   low_wmark_pages(zone),
                   high_wmark_pages(zone),